A wavelength-converting reaction resin compound of the type initially referenced is known from WO 98/12757. A wavelength-converting reaction resin compound is described therein in which an inorganic luminescent pigment powder having grain sizes≦20 μm and a mean grain diameter d50≦5 μm is dispersed in a transparent casting resin.
In the field of light-emitting diodes (LEDs), the use of conversion luminescent materials makes it possible to produce multicolored light by means of a single LED chip. In this process, at least part of the radiation emitted by an LED chip is absorbed by the conversion luminescent material, which then in turn emits radiation of a different wavelength than the absorbed radiation. This radiation emitted by the luminescent material, and radiation emitted by the LED chip and not absorbed by the luminescent material, together then produce the multicolored radiation.
In known light-emitting diode elements made with reaction resin compounds of the type initially referenced, luminescent materials having a density between 4 and 5 g/cm3 are used. The luminescent powders used have luminescent particles whose mean diameter is generally less than 5 μm.
When larger luminescent particles are used in conventionally available reaction resin systems such as epoxy resin, they precipitate during the production process.
In particular during the phase of heating up a resin, shortly before the beginning of the hardening process, its viscosity drops far enough that luminescent particles are no longer held in suspension and precipitate out.
As proposed in WO 98/12757, by adding aerosil to the casting resin for luminescent particles having a mean grain diameter d50≦5 μm, this sedimentation may be reduced sufficiently so that very good distribution of the luminescent particles in the casting resin may be achieved after the hardening process of the casting resin.
With this method of thixotroping by means of aerosil, it is also possible to use luminescent materials with larger particles if larger volumes of aerosil are added. But because adding conventional aerosil reduces the transparency of the resin material, for the conventional types the volume of such aerosil to be added is limited to such a degree that in the case of YAG:Ce luminescent material, for example, the limit of the mean particle diameter is approximately 5 μm.